(CNN) -- Rescuers found four spelunkers "wet and cold" but alive Friday afternoon in a cave in Great Smoky Mountains National Park, a park spokesman said.

Ken Cave said he was told it could take eight to 10 hours to free them from Rainbow Cave, which is entered at the base of a waterfall five miles west of Townsend, Tennessee, where one of the park entrances is located.

He said he didn't know what had kept the four, who weren't identified, in the cave.

"There are a lot of unanswered questions for us right now," Cave said.

Members of an emergency rescue squad from Knoxville, Tennessee, found the men after a 1½-hour trek through the cavern, Cave said. About 13 rescuers were involved.

"They are experienced in cave rescue. In fact, they trained in this cave in the past year," the spokesman said.

Rainbow Cave is in a limestone valley between White Oak Sink and Cades Cove, an area dotted with caves and popular with visitors, Cave said.

The spelunkers -- two 17-year-olds and two men, ages 20 and 24 -- will receive medical attention once freed, he said. A doctor and other medical personnel were at the scene.

The wife of one of the men reported the group missing at 7:30 a.m. Friday.

Cave said the four left Maryville, Tennessee, at 10 p.m. Thursday and were to return by 3 a.m. A backpack and other items were found near the cave, but searchers did not immediately know who they belonged to.

The national park, which covers more than 500,000 acres, is one of the largest wilderness areas in the United States, Ranger Tim Cruze said. It straddles western North Carolina and eastern Tennessee.E-mail to a friend